For convenience, one of those components commonly has a pointer, needle or other reference marker (referred to hereafter for the sake of simplicity as a `reference marker`) designating a reference position on that one component; and the other of the two components commonly has a series of markers or markings spaced apart on a scale, dial, or face (referred to hereafter for the sake of simplicity as a `scale`) and relative to which scale markings the reference marker is relatively movable. The position of one component relative to the other is represented by the position of said reference marker relative to the series of scale markings.
In many cases, (e.g. in clocks and other analogue time-keeping devices, and electrical indicating instruments), the relative positions of the reference marker and the associated series of scale markings is indicative to an observer of the value of a parameter whose magnitude governs or controls the relative positions of the said two components.
In other cases, (e.g. in radio wave-band or other multi-position, operating mode selectors) the relative positions of that reference marker and the associated series of scale markings are indicative to an observer of (a) the relative positions of the two components to which they have been deliberately brought in selecting a desired one of a predetermined plurality of operating modes for an associated apparatus, and hence of (b) the selected operating mode of such apparatus.
In yet other cases (e.g. in linear and other dimension measuring devices) the reference marker may comprise a selected feature of an article, the position of which relative to a datum is to be ascertained in relation to a series of scale markings (constituting a measuring scale) placed adjacent to the article, either directly or by means of a movable probe.
Thus, the present invention relates to various different kinds of analogue indicating means, some of which have been recited above by way of example.
In some such indicating means its is often very difficult to accurately determine the position of the reference marker in relation to the scale markings, for the reason that the reference marker and the associated scale markings are not coplanar, so that the perceived position of the reference marker is dependent upon the position of the observer's eyes, and the interpretation placed upon that perceived position by the observer.
Furthermore, the accurate mass reproduction of such a series of scale markings is difficult and costly to achieve.